The border addressing mode should ideally blend with the border color
when using linear filtering. Until we have a border of pixels around
2D textures, we should probably avoid bleeding pixels from the opposite
edge and just clamp the coordinates.

Change-Id: I7afbb629998732b62413e00ba7bcd55340c7b9bb
Reviewed-on: https://swiftshader-review.googlesource.com/14289Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>